It is preferred in the semiconductor and related arts to utilize large wafers for fabrication of integrated circuits and other devices. Large wafers are preferred inasmuch as an increased number of chips can be fabricated from larger workpieces. As the size of the wafers continues to increase as processing techniques are improved, additional processing obstacles are presented.
For example, it is typically preferred to provide a substantially uniform temperature across the surface of wafers being processed because changes in temperature can influence device fabrication. Wafers of increased diameters and surface areas experience increased temperature fluctuations at various locations on the workpiece. In particular, a partial vacuum is typically used to pull small diameter wafers into direct thermal contact with a hot plate. Such processing methods facilitate substrate temperature control because the substrate temperature is closely associated to the temperature of the hot plate. Fabrication of small sub-micron devices upon larger diameter semiconductor wafers or workpieces requires minimal backside contamination. As such, contact of the workpiece with the hot plate is not typically possible. Large workpieces are processed in conventional operations upon spacers or pins that position the workpiece approximately 0.1 millimeters above the hot plate surface. Such spacing intermediate a chuck or hot plate and the workpiece can result in temperature fluctuations across the surface of the workpiece.
The utilization of specific materials for processing large workpieces in small geometry applications presents numerous obstacles. Absolute workpiece temperature and workpiece temperature uniformity are parameters which are closely monitored during wafer and workpiece fabrication to provide critical dimension (CD) control. Chemically amplified resists are often utilized in deep ultraviolet (DUV) lithography in small micron geometries (eg., 0.25 microns and below). Chemically amplified resists are particularly temperature dependent further increasing the importance of temperature control and monitoring. Some thermal resist processing steps require process windows ranging from 1-2 degrees centigrade down to a few tenths of a degree centigrade. Meteorology that is four to ten times more precise than conventional process equipment is typically utilized to provide thermal performance measurements to 0.1 degrees centigrade.
One approach has disclosed the use of temperature sensors across a surface of the wafer to provide temperature mapping of the workpiece during processing. Platinum foil and copper leads are utilized to electrically connect the temperature sensors. With the use of numerous temperature sensors across an entire workpiece surface, numerous wires are required for coupling and monitoring. Such numerous wired connections can break and/or adversely impact processing of the workpiece or the temperature measurements taken of the surface of the workpiece. Some temperature sensors require four leads per sensor further impacting the processing and temperature monitoring of the workpieces.
An improved method of providing temperature information is disclosed in U.S. patent application Ser. No. 09/032,184, entitled "Electronic Device Workpieces, Methods of Semiconductor Processing and Methods of Sensing Temperature of an Electronic Device Workpiece", filed Feb. 27, 1998, naming Dr. Salman Akram and David R. Hembree as inventors, assigned to the assignee hereof, and incorporated herein by reference.
There exists a need to provide additional improvements for monitoring of processing of workpieces.